This application claims the benefit of a Japanese Patent Application No.2000-354896 filed Nov. 21, 2000, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to flash fixing toners used to visualize electrostatic latent images which are formed by the electrophotography technique and fabrication methods therefor, and more particularly to a flash fixing toner in which an infrared ray absorbing agent is selectively held within a wax and to a fabrication method for fabricating the flash fixing toner.
In image forming apparatuses which employ the electrophotography technique, such as copying machines and printers, it is becoming more popular to make color images. Accordingly, there are demands to improve the image quality which can be obtained and to reduce the cost when using color toners to form color images by flash fixing.
2. Description of the Related Art
According to the electrophotography technique, a uniform electrostatic charge is applied on a photoconductive insulator such as a photoconductive drum, and various means can be used to irradiate an optical image on the photoconductive insulator to thereby form an electrostatic latent image. Then, a toner is used to visualize the electrostatic latent image into a toner image. The toner image is transferred onto a recording medium such as paper, and subjected to a predetermined fixing process to obtain a print having the toner image fixed on the recording medium.
During the fixing process, the toner image on the recording medium is melted and fixed by applying pressure, heat, vapor solvent, light or the like. Of such methods of melting and fixing the toner image, much attention is drawn to the optical fixing method for the following reasons.
First, since the optical fixing method does not require contact to be made with the toner image on the recording medium, the image is unaffected by runs, foreign particles and the like during the fixing process, thereby making it possible to obtain a clear image having a high resolution.
Second, it is unnecessary to wait for a long time after the power of the image forming apparatus is turned ON because there is no need to preheat heater elements or the like, thereby making it is possible to make a quick-start of the image forming apparatus.
Third, even when the recording medium such as paper is jammed within the fixing unit due to a failure of the image forming apparatus, there is no possibility of the recording medium being heated to an extreme and catching fire because the optical fixing method does not require contact to be made with the recording medium, thereby ensuring safe operation of the image forming apparatus.
Fourth, it is possible to carry out the fixing process with respect to various kinds of recording media made of various materials and having various thicknesses, such as sticking paper, preprinted paper and papers of different thicknesses, since the optical fixing method does not require contact to be made with the recording medium.
Generally, the optical fixing method uses xenon flash lamp as the light source to carry out a flash fixing process.
But since the flash fixing process transforms optical energy into thermal energy in order to melt and fix the toner, a poor fixing occurs if the melting of the toner is insufficient. When such a poor fixing occurs, the fixed toner image easily separates from the recording medium when the recording medium is bent or the fixed toner image is rubbed, to thereby deteriorate the quality of the image. In order to prevent such a deterioration of the image quality due to the poor fixing, the toner which is used in the flash fixing process must be designed to absorb the optical energy and sufficiently melt, and to positively permeate the recording medium and to be positively fixed on the recording medium.
In the flash fixing method which uses the xenon flash lamp, the toner is melted by the optical energy of the light having a high intensity in the infrared region. Hence, in this case, the toner must be designed to have an improved infrared absorption so that the toner will sufficiently melt when irradiated with the light having the high intensity in the infrared region.
In the case of black toners, carbon is generally used as the coloring agent. Since carbon has a good light absorption over a wide wavelength region, the light absorption itself of the black toner does not become a problem. Hence, as the measures to be taken to improve the fixing performance of the black toner, the main object is to make the black toner easy to melt, and a highly soluble wax is added as such measures, as proposed in Japanese Laid-Open Patent Applications No.9-22147 and No.9-258471, for example.
On the other hand, in the case of color toners, the light absorption is inevitably lower than that of the black toners, and a poor fixing is more likely to occur in the case of the color toners. Hence, when designing the color toner, it is not only necessary to make the toner easy to melt as in the case of the black toner, but also to improve the light absorption of the color toner.
For example, a Japanese Laid-Open Patent Application No. 61-132959 proposes a method of improving the infrared absorption of the color toner by adding to the color toner an infrared ray absorbing agent which is made of an aminium-salt-based compound and a diimonium-salt-based compound. Generally, a compound having a high infrared absorption has a hue ranging from brown to black. However, since the aminium-salt-based compound or the like not only has a high infrared absorption but is also capable of indicating a light color tone in the visible region, the effect on the original hue of the color toner is small, and the aminium-salt-based compound or the like is considered a good additive for supplementing the light absorption of the color toner.
The infrared ray absorbing agent such as the aminium-salt-based compound is an ionic compound having a high polarity. For this reason, the aminium-salt-based compound or the like has a high compatibility with resins such as polyester and styrene-acrylic which also have a high polarity and are generally used as a binder resin of the toner. In addition, a charge control agent is added to the toner to control the charge thereof, and this charge control agent also has a polarity. Accordingly, when the infrared ray absorbing agent and the charge control agent both having polarities contact each other within the binder resin, a reaction may cause undesirable effects on the charge control characteristic of the toner.
Furthermore, the infrared ray absorbing agent deteriorates the resulting infrared absorption. In order to obtain a desirable fixing performance of the color toner, it is necessary to add a large amount of infrared ray absorbing agent in the toner, but this affects the hue of the toner even when a light colored infrared ray absorbing agent such as the aminium-salt-based compound is used. Moreover, the fabrication cost of the toner becomes high when a large amount of infrared ray absorbing agent is added to the toner.
Accordingly, it is a general object of the present invention to provide a novel and useful flash fixing toner and fabrication method therefor, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a flash fixing toner having a good charge control characteristic, a high infrared absorption and a relatively low cost, and capable of realizing a flash fixing process which obtains a high-quality image which is satisfactorily fixed, and a fabrication method for fabricating such a flash fixing toner.
Still another object of the present invention is to provide a flash fixing toner comprising a binder resin, a coloring agent, a charge control agent, a wax, and an infrared ray absorbing agent, where the infrared ray absorbing agent is held within the wax. According to the flash fixing toner of the present invention, the infrared ray absorbing agent is selectively held within the wax, and the contact between the infrared ray absorbing agent and the charge control agent is suppressed. For this reason, both the infrared ray absorbing agent and the charge control agent can sufficiently exhibit the respective original functions. As a result, the charge control characteristic of the toner becomes satisfactory, and the infrared absorption becomes satisfactory to positively melt the toner upon infrared ray irradiation. Consequently, the toner can realize a high resolution and a high fixing performance. On the other hand, since the infrared ray absorbing agent and the charge control agent will not mutually react and cause mutual deterioration, it is possible to suppress the amount of these agents to be added to the toner, to thereby enable the cost of the toner to be reduced.
The wax may be dotted in a form of islands within the binder resin. In addition, the wax may be made of a material or a mixture of materials selected from a group of polyolefins, fatty esters, paraffin wax, carnauba wax, amide-based wax and acid-converted polyethylene. In these cases, the possibility of contact between the infrared ray absorbing agent and the charge control agent is greatly reduced when compared to the conventional case where the infrared ray absorbing agent is randomly dispersed.
The infrared ray absorbing agent may be made of an aminium-salt-based compound and or a diimonium-salt-based compound. In this case, it is possible to positively melt the toner upon infrared ray irradiation.
Further, the flash fixing toner may further comprise a surface-active agent within the wax. In this case, it is possible to realize a state where the surface-active agent functions to hold the infrared ray absorbing agent having polarity within the wax.
A further object of the present invention is to provide a fabrication method for fabricating a flash fixing toner, comprising a first step which melts and mixes a wax, an infrared ray absorbing agent and a surface-active agent to obtain a mixture, and forms the mixture into a powder of wax grains including the infrared ray absorbing agent, and a second step which mixes the wax grains including the infrared ray absorbing agent, a binder resin, a coloring agent and a charge control agent, and forms a powder of color toner grains forming the flash fixing toner. According to the fabrication method of the present invention, it is possible to fabricate a toner which can realize a high resolution and a high fixing performance.